Articular surface implant and delivery system

ABSTRACT

A method is provided for delivering an implant for replacing a portion of an articular surface. The method may include forming a socket in an articulating feature that is capable of moving relative to the articular surface. An implant may be placed in the socket and the articulating feature may be moved relative to the articular surface to generally align the socket with an implant site formed in the articular surface. The implant may be transferred from the socket into the implant site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application under 37 CFR §1.53(b) of U.S. application Ser. No. 11/359,892 filed Feb. 22, 2006, now U.S. Pat. No. 7,828,853, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/654,928, filed on Feb. 22, 2005, and is a continuation in part of U.S. patent application Ser. No. 10/994,453, filed Nov. 22, 2004, the entire disclosures of which are incorporated herein by reference.

FIELD

The present disclosure is directed at implants for replacing a portion of an articular surface of a joint and systems and method for delivering implants to an implant site.

BACKGROUND

Articular cartilage, found at the ends of articulating bone in the body, is typically composed of hyaline cartilage, which has many unique properties that allow it to function effectively as a smooth and lubricious load bearing surface. Hyaline cartilage problems, particularly in knee, hip joints, and should joints, are generally caused by disease such as occurs with rheumatoid arthritis or wear and tear (osteoarthritis), or secondary to an injury, either acute (sudden), or recurrent and chronic (ongoing). Such cartilage disease or deterioration can compromise the articular surface causing pain and eventually, loss of joint movement. As a result, various methods have been developed to treat and repair damaged or destroyed articular cartilage.

For smaller defects, traditional options for this type of problem include leaving the lesions or injury alone and living with it, or performing a procedure called abrasion arthroplasty or abrasion chondralplasty. The principle behind this procedure is to attempt to stimulate natural healing. The bone surface is drilled using a high speed rotary burr or shaving device and the surgeon removes about 1 mm of bone from the surface of the lesion. This creates an exposed subchondral bone bed that will bleed and will initiate a fibrocartilage healing response. One problem with this procedure is that the exposed bone is not as smooth as it originally was following the drilling and burring which tends to leave a series of ridges and valleys, affecting the durability of the fibrocartilage response. Further, although this procedure can provide good short term results, (1-3 years), fibrocartilage is seldom able to support long-term weight bearing and is prone to wear, soften and deteriorate.

Another procedure, called Microfracture incorporates some of the principles of drilling, abrasion and chondralplasty. During the procedure, the calcified cartilage layer of the chondral defect is removed. Several pathways or “microfractures” are created to the subchondral bleeding bone bed by impacting a metal pick or surgical awl at a minimum number of locations within the lesion. By establishing bleeding in the lesion and by creating a pathway to the subchondral bone, a fibrocartilage healing response is initiated, forming a replacement surface. Results for this technique may be expected to be similar to abrasion chondralplasty.

Another means used to treat damaged articular cartilage is a cartilage transplant. Essentially, this procedure involves moving cartilage from an outside source or other knee or from within the same knee into the defect. Typically, this is done by transferring a peg of cartilage with underlying bone and fixing it in place with a screw or pin or by a press fit. Although useful for smaller defects, large defects present a problem, as this procedure requires donor pegs proportionate to the recipient bed. Large diameter lesions may exceed the capacity to borrow from within the same knee joint and rule out borrowing from another source.

Larger defects, however, generally require a more aggressive intervention. Typically treatment requires replacing a portion or all of the articular surface with an implant or prosthetic having an outer layer that that is polished or composed of a material that provides a lubricious load bearing surface in approximation of an undamaged cartilage surface. Replacement of a portion, or all, of the articular surface requires first cutting, boring, or reaming the damaged area to remove the damaged cartilage. A recess to receive an implant or prosthetic is formed at the damaged site. The implant or prosthetic is then secured to the bone in an appropriate position in the recess.

The treatment and/or replacement procedure often requires direct access to the damaged surface of the cartilage. While the most commonly damaged portions of some joints may easily be accessed for repair using a minimally invasive procedure some joints are not nearly as accessible. For example, the superior or medial femoral head, the medial humeral head, the glenoid, etc. do not permit direct access sufficient to carry out replacement of the articular surface in a minimally invasive manner. In fact, repair of such obstructed joints often requires an invasive procedure and necessitates complete dislocation of the joint. Procedures of such an invasive nature may be painful and require an extended recovery period. completely dislocating the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosed subject matter will be apparent from the following descriptions of embodiments consistent therewith, which description should be considered in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of an embodiment of an implant consistent with the present disclosure positioned to replace a portion of an articular surface;

FIG. 2 is a top perspective view of an embodiment of an implant consistent with the present disclosure;

FIG. 3 is a bottom perspective of an embodiment of an implant consistent with the present disclosure;

FIG. 4 is a top perspective of an embodiment of an implant consistent with the present disclosure representationally depicting surface geometry defining contours;

FIG. 5 shows an embodiment of an implant loaded in a socket of a cooperating articulating feature consistent with a system of delivering an implant according to the present disclosure;

FIG. 6 shows the cooperating articulating feature positioned to align an implant with an implant site in the articular surface consistent with a system of delivering an implant according to the present disclosure; and

FIG. 7 depicts the installation of an implant according to the present disclosure into an implant site in an articular surface consistent with a system of delivering an implant according to the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 4 illustrate an embodiment of an implant 100 consistent with the present disclosure from various views. In FIG. 1 the implant 100 is shown installed in an implant site 101 and replacing at least a portion of an articular surface 103, e.g. of a bone 105. In the illustrated embodiment of FIG. 1 the bone 105 is generally show as being a tibia. The implant 100 is depicted replacing at least a portion of the articular surface of the tibia corresponding to a portion of the knee joint. While an implant herein may suitably be employed to replace a portion of an articular surface of a knee joint, the present disclosure should not be interpreted as being limited to replacing a portion of a tibial articular surface in a knee joint. An implant herein may suitably be employed to replace at least a portion of other articular surfaces without limitation.

As shown, the implant 100 may generally include an implant body 102. The implant body 102 may include a load bearing surface 104 at one end of the implant body 102. The load bearing surface 104 may be a surface configured to interact with a cooperating articulating feature. The proximal end 106 of the implant body 102, opposite the load bearing surface 104, may be provided having a generally tapered and/or conical profile. In further embodiments, the proximal end 106 may have a generally truncated conical profile.

As best shown in FIG. 3, the implant body 102 may have a generally cylindrical shape. Accordingly, the implant 100 may have a generally circular cross-sectional shape and may be axially symmetrical. In other embodiments, the implant may have an oval or other cross-sectional shape. Consistent with the illustrated embodiment, the load bearing face 104 of the implant 100 may be oriented at an angle relative to the axis of the cylindrical implant body 102. As best observed in FIGS. 2 and 4, the angular orientation of the load bearing surface 104 relative to the axis of the implant body 102 may provide the load bearing surface 104 having a generally elliptical and/or oval shape.

The angular relationship of the load bearing surface 104 relative to the axis of the implant body 102 may be varied according to specific applications. According to one aspect, the angle of the load bearing surface 104 relative to the axis of the implant body 102 may be related to the configuration and/or angle of the implant site 101 to the portion of the articular surface 103 to be replaced. Accordingly, depending upon the relationship between the portion of the articular surface 103 to be replaced and the implant site 101, the angular relationship between the load bearing surface 104 and the axis of the implant body 102 may vary between a very shallow angle, e.g., less than 45 degrees, up to a perpendicular orientation. In the specific illustrated embodiment, the load bearing surface 104 may be at an angle of about 60 degrees relative to the implant body 102. As the angle of the load bearing surface 104 relative to the implant body 102 is application specific, an implant 100 consistent with the present disclosure should not be considered to be limited by any particular angular relationship.

From a general perspective, the load bearing surface 104 may have a contour and/or geometry that may be capable of cooperating with an interacting articulating surface and/or feature. In one embodiment, the interacting articulating surface and/or feature may include an interacting articular surface of a joint. For example, in an embodiment in which the implant may be employed to replace at least a portion of an articular surface of a tibia, the load bearing surface of the implant may have a contour and/or geometry that may be capable of cooperating with an interacting articular surface of a femur. According to a further embodiment, such as may occur in a uni-compartmental and/or total knee replacement, the implant may be employed to replace at least a portion of the articular surface of a tibia. The load bearing surface of the implant may have a geometry capable of cooperating with an interacting implant replacing at least a portion of an articular surface of a femur. Consistent with the present disclosure, the implant may suitable be employed to replace at least a portion of various articular surfaces in addition to a portion of an articular surface of a tibia. For example, an implant herein may suitably be employed to replace a portion of an articular surface of a knee joint, a hip joint, a shoulder joint, etc. Accordingly, the foregoing example should not be construed as limiting on the application of an implant consistent with the present disclosure.

Consistent with the foregoing, an implant may include a load bearing surface having a contour and/or geometry that may be capable of cooperating with an interacting articulating surface. As such, the load bearing surface may have a contour and/or geometry that may generally approximate and/or be based on a contour and/or geometry of the portion of the articular surface being replaced by the implant. In an embodiment, the portion of the articular surface being replaced may be mapped using various know techniques to quantitatively and/or qualitatively represent the contour and/or geometry of the portion of the articular surface that may be replaced by the implant. An implant may be constructed and/or selected from a set of implants having various contours and/or geometries. Consistent with such an embodiment, the load bearing surface of the implant may be based on the contour and/or geometry of the portion of the articular surface to be replaced by the implant. In an alternative embodiment, an implant may be fabricated or selected from a set of standard size and/or shape implants to provide a general approximation of the articular surface being replaced. Selection or fabrication of an implant may rely on various degrees of quantitative reference to the articular surface being replaced, including no quantitative reference to the articular surface.

Different articular surfaces and/or different regions of an articular surface may be susceptible to replacement by implants having a load bearing surface various contours and/or geometries. In some applications a convex load bearing surface may be suitable. In other applications a planar, concave, and/or compound curved load bearing surface may provide a suitable implant load bearing surface geometry.

Referring to FIG. 4, the geometry of the load bearing surface 104 of the implant 100 may generally be defined by a first curve 108 and a second curve 110. Consistent with the illustrated embodiment, the first and second curves 108, 110 generally defining the contour and/or geometry of the load bearing surface 104 may have a generally perpendicular orientation to one another. Various other angular relationships between the first and second 108, 110 curves may also suitably be employed. In one embodiment the load bearing surface 104 may have a contour and/or geometry resulting from a faired transition between the first curve 108 and the second curve 110. That is, the contour and/or geometry of the load bearing surface 104 may be provided by a smooth transition between the first curve 108 and the second curve 110 at each quadrant between the first curve 108 and the second curve 110.

According to another embodiment, the load bearing surface 104 may have a contour and/or geometry corresponding to the second curve 110 lofted along the first curve 108. In one such embodiment, the contour and/or geometry of the load bearing surface 104 may be achieved by sweeping the second curve 110 along the first curve 108 while maintaining the second curve 110 normal to the first curve 108. In such an embodiment, the first curve 108 may be provided in a first plane, e.g. a plane defined by the X and Z axis. The second curve 110 may be provided in a perpendicular plane. The angular pitch of the perpendicular plane relative to the first plane may vary along the first curve 108 to maintain the second curve 110 normal to the first curve 108 along the sweep of the first curve 108. According to another embodiment, the second curve 110 may be swept along the first curve 108 with the first curve 108 and the second curve 110 in orthogonal planes. For example, the first curve 108 may be provided in a first plane, e.g., a plane defined by the Y and Z axis and the second curve may be provided in an orthogonal plane, e.g., a plane defined by the X and Z axis.

In one aspect, the first and second curves 108, 110 may generally correspond to measurements of the curvature and/or geometry of the portion of the articular surface 103 to be replaced by the implant 100. In such an embodiment, perpendicular measurements of the contour and/or geometry of the portion of the articular surface 103 to be replaced may be taken. Measurement of the contour and/or geometry of the portion of the articular surface 103 to be replaced by the implant 100 may be achieved using direct contour mapping of the articular surface 103 and/or using various imaging techniques, such as radiological imaging techniques.

The implant 100 may include a relieved edge 112 around the perimeter of the load bearing surface 104. The relieved edge 112 may include a rounded over, e.g., radiused, edge, a chamfer edge, etc. According to one aspect, when the implant 100 is installed in an articular surface 103 and replacing at least a portion of the articular surface 103, the relieved edge 112 around the load bearing surface 104 may reduce the presence of a hard edge at a transition between the implant 100 and surrounding articular surface 103. A reduction and/or elimination of a hard edge at the transition between the load bearing surface 104 of the implant 100 and the surrounding articular surface 103 may reduce and/or eliminate scraping of an interacting articular surface during articulation of the joint. Additionally, the relieved edge 112 may accommodate manufacturing and/or installation tolerances. The relieved edge 112 may permit smooth operation of the joint in a situation in which the implant 100 sits slightly proud above and/or slightly recessed below the surrounding articular surface 103.

As shown, the implant 100 may include a plurality of grooves 114 on the exterior surface of the implant body 102. The grooves 114 may facilitate anchoring the implant 100 in position in an implant site 101 created in the articular surface 103 and the underlying bone 105. Consistent with an embodiment herein, the implant 100 may be secured, at least in part, in the implant site 101 using bone cement. When the implant 100 is installed into the implant site 101 using bone content, the bone cement may be squeezed, forced, and/or caused to flow to at least partially fill at least a portion of one of the grooves 114. The bone cement at least partially filling at least a portion of one of the grooves 114 may provide a mechanical lock between the bone cement and the grooves 114 in the implant body 102. The mechanical lock between the bone cement and the implant 100 may assist in securing the implant 100 in position in the implant site 101. Additionally, the mechanical lock between the bone cement and the grooves 114 may assist in retaining the implant 100 in the implant site 101 in the event of a partial and/or total adhesive failure between the bone cement and the implant.

Similar to the grooves 114 in the implant body 102, the proximal end 106 of the implant 100 may also include one or more grooves 116. The grooves 116 in the proximal end of the implant 100 may provide a mechanical lock between bone cement and the implant 100. In one embodiment, the grooves 114 in the implant body 102 and/or the grooves 116 in the proximal end 106 of the implant 100 may include an undercut region. The undercut region may increase the mechanical lock achieved between the bone cement and the implant 100.

An implant 100 herein may be formed from various different biologically compatible materials. The material of the implant may be selected to provide various properties, combinations of properties, and/or compromises between desired properties. For example, the implant may be formed from a metallic material, such as stainless steel, titanium, and/or various other biologically compatible metals and alloys. Metallic materials may provide strength and wear resistance. The load bearing surface of the implant may be polished to provide a relatively low friction surface for cooperating with an interacting articulating feature. Polymeric and/or polymeric based materials, such as ultra-high molecular weight polyethylene, polyethylene, polyvinyl alcohol hydrogel, etc., may also be employed for producing an implant herein. Such polymeric and/or polymer based materials may provide lubricious and/or low friction surfaces, as may be suitable for cooperating with interacting articular features. Additionally, polymeric and/or polymeric based materials may provide some degree of impact cushioning and/or impact absorption. In still further embodiments, the implant may be provided as an assembly including more than one material. For example, the implant may include a body portion formed from a metallic material having a load bearing surface formed from a polymeric and/or polymeric based material. Various other materials may also suitably be employed for producing an implant herein.

An implant consistent with the present disclosure may be produce using a variety of manufacturing techniques. According to one embodiment, the implant may be produced from cylindrical rod stock. The rod stock may be cut at an angle relative to axis of the rod stock, thereby providing a load bearing surface. The rod stock may further be tapered, e.g., by turning on a lathe, to provide a conical proximal end. Features, such as the grooves in the implant body and the proximal end, as well as the relieved edge of the load bearing surface, may subsequently be machined into the implant. In alternative embodiments, the implant may be produced by machining from a blank and/or billet of material. Furthermore, the implant may be produced using various molding processes, such as metal, ceramic and/or polymer casting. Other molding techniques may include metal injection molding, polymer injection molding, etc. Various other manufacturing processes and techniques may also be employed.

Turning next to FIGS. 5 through 7, and embodiment of a system for delivering an implant 100 to an implant site 101 is shown. As depicted, the implant site 101 may be formed in an articular surface 101 and the underlying bone 105. In one embodiment, the implant site 101 may be formed using a retrograde procedure, in which an access tunnel 107 may be created extending through at least a portion of the bone 105. An expanding cutter may be inserted into the access tunnel and a portion of the articular surface 101 and underlying bone 105 may be excised using the expanding cutter. Examples of suitable methods for creating an implant site are disclosed, for example, in U.S. provisional patent application Ser. Nos. 60/583,549, filed on Jun. 28, 2004, and 60/641,552, filed on Jan. 5, 2005. Various other retrograde and/or direct access methods may also suitably be employed for creating an implant site.

Consistent with the illustrated delivery system, the implant 100 may be delivered to the implant site 101 using a cooperating articulating feature 200 as a carrier. In the illustrated embodiment, the implant site 101 may be formed in the articular surface 103 and underlying bone 105 of a tibia. In such and embodiment, the cooperating articulating feature 200 may be an articular surface of a femur. A socket 202, sized to at least partially receive the implant 100, may be formed in the cooperating articulating feature 200. The socket 202 may be formed by drilling, cutting, and/or using other suitable excision techniques.

The cooperating articulating feature 200 may be positioned relative to the articular surface 103 so as to expose the socket 202 in the cooperating articulating feature. In the illustrated embodiment, in which the implant 100 is to be installed in an implant site 101 in a tibia, the knee may be positioned at approximately 80-90 degrees of flexion, thereby exposing the socket formed in the articular surface of the femur. Various other angular relationships may also and/or alternatively suitably be employed. With the socket 202 in the cooperating articulating feature 200 exposed, the implant 100 may be placed in the socket 202. As shown in FIG. 5, the implant 100 may generally be placed in the socket 202 with the load bearing surface 104 facing inward and the implant body 102 and proximal end 106 facing outwardly relative to the socket 202.

Turning to FIG. 6, the cooperating articulating features 200 may be moved relative to the articular surface 103 to generally align the socket 202 in the cooperating articulating feature 200 with the implant site 101 in the articular surface 103. In this manner, the socket 202 in the cooperating articulating feature 200 may generally serve as a carrier for conveying the implant 100 to the implant site 101. In the illustrated embodiment, the knee may be moved to approximately 0-10 degrees of extension. In such an orientation the socket in the femur may be generally aligned with the implant site in the articular surface of the tibia. Depending upon the location of the socket in the femur and the location of the implant site in tibia, the angular orientation, e.g., the angle of extension of a knee, necessary to generally align the socket and the implant site may vary. As such, the angular orientation should not be understood to be limiting on the system herein.

With the socket 202 in the cooperating articulating feature 200 generally aligned with the implant site 101 in the articular surface, the implant 100 may be transferred from the socket 202 to the implant site 103, as shown in FIG. 7. Consistent with the illustrated embodiment, the implant 100 may be transferred to the implant site 101 via a tether 204. As shown, the tether 204 may be coupled to the implant 100 and may extend from the implant site 101 to the exterior of the bone 105 through the access tunnel 107. The tether 204 may be withdrawn through the access tunnel 107, thereby drawing the implant 100 into the implant site 101. According to another embodiment, the implant 100 may be pushed from the socket 202 and seated in the implant site 101 using an implement introduced in between the articular surface 103 and the cooperating articulating feature 200.

As mentioned previously, the implant 100 may be secured in the implant site, at least in part, using bone cement. The bone cement may be applied to the implant 100 and/or to the implant site 101 prior to transferring the implant 100 from the socket 202 to the implant site 101. Alternatively, bone cement may be introduced between the implant 100 and the implant site prior to fully seating the implant 100. The bone cement may be introduced in between the implant 100 and the implant site 101 through the access tunnel 107, and/or from the exterior of the implant site 101 adjacent to the articular surface. Various additional and/or alternative fixturing and/or securement techniques may be employed for securing the implant 100 in position in the implant site 101.

In summary, according to one aspect, the present disclosure may provide a method for delivering an articular surface implant. The method may include forming an implant site in an articular surface, in which the implant site is capable of receiving an implant for replacing at least a portion of the articular surface. The method may also include forming a socket in an articulating feature capable of moving relative to the articular surface, and disposing the implant at least partially in the socket. The method may also include generally aligning the socket and the implant site, and transferring the implant from the socket at least partially into the implant site.

According to another aspect, the present disclosure may provide a method of replacing a portion an articular surface of a tibia. The method may include excising an implant site in the articular surface of the tibia, and excising a socket in an articular surface of a femur adjacent to the tibia. The method may also include disposing an implant capable of replacing at least a portion of the articular surface of the tibia in the socket. The method may further include articulating the femur relative to the tibia to generally align the socket and the implant site, and transferring the implant from the socket at least partially into the implant site.

The illustrated system is directed at delivering an implant for replacing at least a portion of an articular surface of a tibia. In the particular illustrated embodiment, the implant may be accommodated in a socket formed in a femoral articular surface and the femur may be articulated relative to the tibia to generally bring the socket in the formal articular surface into alignment with the implant site in the tibial articular surface. With the socket in the femoral articular surface generally aligned with the implant site in the tibial articular surface, the implant may be transferred from the socket in the femoral articular surface to the implant site in the tibial articular surface. However, from a broader perspective, a system consistent with the present disclosure may generally include disposing an implant in a socket, cutout, or natural recess in a cooperating articulating feature and moving the feature to align the implant in the socket with an implant site in an articular surface and transferring the implant from the socket to the implant site. Accordingly, the system herein is susceptible to broader application than the delivery of an implant to an implant site in an articular surface. For example, the system herein may be used to deliver an implant to an articular surface of a hip joint, shoulder joint, elbow, etc. The scope of the present disclosure should not, therefore, be limited to the specific embodiments disclosed therein. 

What is claimed:
 1. A system for repairing a joint including a first and a second bone having at least a first and a second articular surface, respectively, said system comprising: a drill guide comprising: a locating feature configured to be disposed on said first articular surface proximate to a defect on said first articular surface; a drill bushing defining a working axis extending through said locating feature; and an arm co-axially aligning said locating feature and said drill bushing; a drill bit configured to be received at least partially through said drill bushing along said working axis to drill a passage through said first bone and provide an opening on said first articular surface about said defect; a tether configured to be partially disposed within said passage in said first bone; a reamer comprising a shaft and a cutter configured to excise an implant site in a portion of said first articular surface about said defect having a diameter larger than said passage; an implant configured to be at least partially received in said implant site via said tether extending through said passage in said first bone, wherein said implant comprises an implant body and a load bearing surface disposed about a first end of said implant body, said load bearing surface having a contour substantially corresponding to a contour of said portion of said first articular surface about said defect.
 2. The system of claim 1, wherein said reamer is configured to be removably coupled to said drive shaft extending through said passage.
 3. The system of claim 1, wherein said entire implant is received within said implant site such that said load bearing surface is substantially flush with said surrounding first articular surface.
 4. The system of claim 1, wherein said implant comprises a generally circular cross-sectional shape.
 5. The system of claim 4, wherein said implant is axially symmetrical.
 6. The system of claim 4, wherein said implant body further comprises a generally cylindrical implant body wherein said load bearing surface is disposed about a first end of said implant body wherein said implant further includes a proximal end disposed generally about a second end of said implant body generally opposite said first end, said proximal end having a generally tapered profile.
 7. The system of claim 6, wherein said load bearing surface is orientated at an angle relative to a longitudinal axis of said implant body such that said load bearing surface has a generally elliptical shape.
 8. The system of claim 7, wherein said angular relationship between said load bearing surface and said longitudinal axis of said implant body is less than 45 degrees.
 9. The system of claim 7, wherein said angular relationship between said load bearing surface and said longitudinal axis of said implant body is between 45 degrees and 90degrees.
 10. The system of claim 7, wherein said angular relationship between said load bearing surface and said longitudinal axis of said implant body is about 60 degrees.
 11. The system of claim 1, wherein said implant comprises an oval cross-sectional shape.
 12. The system of claim 1, further comprising a relieved edge around a perimeter of said load bearing surface of said implant.
 13. The system of claim 1, further comprising a plurality of implant body grooves on an exterior surface of an implant body of said implant.
 14. The system of claim 13, further comprising bone cement configured to be disposed in said implant site and within said plurality of implant body grooves in said implant body.
 15. The system of claim 13, wherein said plurality of implant body grooves further include an undercut region.
 16. The system of claim 1, wherein a proximal end of said implant generally opposite said load bearing surface comprises a plurality of proximal end grooves.
 17. The system of claim 16, wherein said plurality of proximal end grooves further include an undercut region.
 18. The system of claim 1, further comprising an excision device configured to form a socket in an articulating feature associated with said second articular surface of said second bone, wherein said socket is exposed relative to said first articular surface of said first bone when in a first position and is generally aligned with implant site when in a second position.
 19. The system of claim 1, wherein said reamer is configured to form a socket in said second articular surface.
 20. The system of claim 1, wherein at least a portion of said reamer is further configured to be coupled to said tether and configured to be conveyed to said first articular surface by said tether.
 21. The system of claim 20, wherein said cutter is configured to be coupled to said tether.
 22. The system of claim 1, wherein said reamer comprises an expanding cutter.
 23. The system of claim 1, wherein said shaft includes a cannulated shaft configured to receive a portion of said tether.
 24. The system of claim 23, wherein said tether is disposed within said cannulated shaft and is configured to convey said cutter to a distal end of said shaft.
 25. The system of claim 23, wherein said tether is disposed within said cannulated shaft and is configured to convey said implant to said implant site.
 26. The system of claim 1, wherein said load bearing surface of said implant is generally defined by a first curve and a second curve disposed generally perpendicularly to said first curve.
 27. A method of replacing a portion an articular surface of a joint including a first and a second bone having at least a first and a second articular surface, respectively, said method comprising: excising an implant site in a portion of said articular surface of said first bone; excising a socket in an articular surface of said second bone adjacent to said first bone; disposing at least a portion of an implant within said socket, wherein said implant comprises an implant body and a load bearing surface disposed about a first end of said implant body, said load bearing surface having a contour substantially corresponding to a contour of said portion of said articular surface of said first bone; articulating said first bone and said second bone from a first position, wherein said socket is exposed relative to said articular surface of said first bone and is configured to receive said implant, to a second position, wherein said socket is generally aligned with said implant site; and transferring said implant from said socket at least partially into said implant site. 